A typical circuit board assembly includes a circuit board (i.e., layers of conductive and non-conductive material sandwiched together), and a variety of circuit board components which mount to the circuit board. Examples of circuit board components include, among other things, integrated circuits (ICs), individual circuit elements (e.g., resistors, capacitors, etc.), and connectors. Some components (e.g., lead frame packages, individual resistors, electrical connectors, etc) have leads which insert into and solder to sets of plated-through holes which extend through the circuit board. Other components (e.g., Ball Grid Array (BGA) packages, ceramic chips, etc.) solder to sets of surface mounting technology (SMT) pads or contacts disposed on the surface of the circuit board.
Some components include relatively large-sized packages such as BGA packages which, in some instances, can be approximately two inches by two inches (or more) in area. Contacts from such large-sized packages (e.g., solder balls) typically solder to square-shaped, round or octagon-shaped SMT pads. Examples of circuits which commonly reside in such large-sized packages include large scale integrated circuits such as microprocessor circuits, application specific integrated circuits (ASICs), and field programmable gate arrays (FPGAs).
In contrast, some components include relatively small-sized packages such as standard 0402, 0603 and 0805 ceramic chip packages which are set forth by the Electronics Industries Alliance (EIA). The contacts from such small-sized packages (e.g., the end terminals) typically solder to rectangle-shaped SMT pads disposed on the surfaces of the circuit boards. Examples of circuits which commonly reside in such small-sized packages include individual capacitor and diode circuits.
There are a variety of conventional approaches to soldering small-sized circuit board components to circuit boards. One conventional approach for soldering a small-sized circuit board component to SMT pads of a circuit board is called the “pre-glued approach”. To illustrate the pre-glued approach, suppose that a circuit board manufacturer wishes to mount a diode contained in a standard 0603 package between two rectangle-shaped pads on a circuit board. First, the manufacturer places a drop of glue onto the surface of the circuit board between the two rectangle-shaped pads. Next, the manufacturer reads polarity ink markings printed on the surface of the circuit board (e.g., white ink printed over green FR4 material of the circuit board) to determine the proper orientation of the diode. Then, based on the ink markings, the manufacturer places the diode in contact with the drop of glue such that the anode of the diode sits over one rectangle-shaped pad and the cathode of the diode sits over the other rectangle-shaped pad. The manufacturer can repeat this step (e.g., in an automated manner using automated equipment) for other small-sized components.
After the glue has dried and now holds the diode in place, the manufacturer typically turns the circuit board over (i.e., upside down), and places other larger-sized circuit board components into their corresponding soldering positions on the circuit board and passes the circuit board structure through a wave soldering system. As components pass over the solder wave, solder from the solder wave wets to the contacts of both the components and the circuit board to solder the components to the circuit board. In particular, solder from the solder wave flows between the terminals of the diode package and the two rectangular-shaped pads to solder the diode package to the circuit board. During the wave soldering process, the drop of glue continues to hold the diode package in place thus preventing the package from inadvertently moving out of its earlier-placed position.
Another conventional approach to soldering a small-sized circuit board component to a circuit board is called the “printed paste approach”. To illustrate the printed paste approach, suppose that a circuit board manufacture wishes (i) to initially solder a diode having a small-sized circuit board component package (along with perhaps other similar-sized components) to a first side of the circuit board during a first heating process, and (ii) to subsequently solder larger-sized circuit board components to a second side of the circuit board structure during a second heating process. To this end, the manufacturer typically prints solder paste over two rectangle-shaped SMT pads on the first side of the circuit board structure, identifies the proper orientation of the diode based on polarity ink markings printed on the first side, and places the anode and the cathode of the diode in contact with the printed paste and over the appropriate rectangle-shaped SMT pads based on the printed polarity ink markings. The manufacturer may repeat this step for other similar-sized components that it wishes to mount to the first side. The manufacturer then passes the circuit board through an oven in order to activate flux and melt solder within the printed solder paste and thus solder the diode terminals to the two rectangle-shaped SMT pads (as well as perhaps solder other components to other pads).
After the circuit board has cooled to form solder joints between each component and the first side of the circuit board, the manufacturer flips the circuit board over, prints solder paste on the second side of the circuit board, places additional components in contact with the printed paste over their corresponding mounting locations (e.g., large-sized components), and passes the circuit board through the oven a second time to solder the additional components to the second side of the circuit board. During this second heating phase, the solder joints on the first side of the circuit board tend to re-flow but surface tension provided by the solder, which is wetted to both the rectangle-shaped soldering pads and the component terminals, tends to prevent the earlier-soldered components (e.g., the diode) from falling off the first surface of the circuit board. Accordingly, when the circuit board finally cools, mounted components reside on both sides of the circuit board.